The present invention relates to a power-generation detection circuit and, in particular, to power-generation detection for use in an electronic device which is driven by an AC power generated by motion of a rotating weight or motion of a spring. The invention further relates to a semiconductor device in which the power-generation detection circuit is formed. And more in particular an electronic device, having the power-generation detection circuit, which is a timepiece and a power-generation detection method and a power consumption control method for operating the electronic device.
In a compact portable electronic device, such as a wrist watch, it is known to incorporate a power-generation device therein to obtain power for driving the electronic device without a battery. Referring now to FIG. 15, there is shown a simplified configuration of an electronic device which incorporates a power-generation device 6. This portable electronic device includes an electromagnetic power-generation device as the power-generation device 6. Power-generation device 6 includes a rotating weight 7 that moves in a swinging motion when the electronic device is moved or shaken, a train wheel mechanism 8 for transmitting the rotating motion of rotating weight 7, a stator 9 and a rotor 10. When rotor 10 rotates, an electromotive force is generated by an output coil 11 of stator 9, so that an AC power is output. In addition, the AC power output from electromagnetic generator 6 is full-wave rectified by a rectification diode bridge 12 to supply the power to a large-capacity capacitor 13 and a circuit unit 14 of the electronic device. When no power generation is performed by electromagnetic generator 6, circuit unit 14 is driven by power stored in large-capacity capacitor 13. For this reason, the portable electronic device can continuously operate circuit unit 14 without a battery.
Because the electronic device described above has no means for detecting the state of power generation supplied from power-generation device 6, the current consumption of circuit unit 14 is constant regardless of the state of power generation of power-generation device 6. As a result, power is consumed by circuit unit 14 even while no power is being generated by power-generation device 6. This may result in large-capacity capacitor 13 being discharged within a short period of time with the possibility of circuit unit 14 stopping completely.